The present invention relates to a mobile communication system and a mobile communication method which is capable of reducing xe2x80x9cservice disable periodxe2x80x9d occurring when the communication terminal side switches systems in a communication terminal side which is capable of utilizing a plurality of radio communication system.
In a communication terminal which is capable of utilizing a plurality of radio communication system, when one system is switched to another system at the communication terminal side, even if these systems have similar electromagnetic wave (electric wave) environments, the operation starts from the normal initial sequences of the respective systems.
For that reason, for example, in the case where a user intends to switch from a system 1 to a system 2, a long period of time is required until a line on the system 2 side is acquired and the service of the system 2 can be actually supplied to the user.
In more detail, as shown in FIG. 12, the initial sequence is roughly classified into (1) tracking in Steps 20 to 22 (in the case where an antenna having directivity is used), (2) frequency correction in Steps 23 to 24, and (3) evaluation of a radio line in Steps 25 to 27. Hereinafter, the respective processes will be described with reference to specific examples.
FIG. 11 shows an arrangement of a conventional mobile communication terminal. In the figure, reference numeral 1 denotes an antenna for transmitting and receiving electromagnetic waves; 2, a tracking unit for directing the orientation of the antenna 1 to an arrival direction of the electromagnetic waves; 3, a receiver for demodulating the received electromagnetic waves; 4, a transmitter for modulating the contents to be transmitted to electromagnetic waves; 5, a handset for conducting indication for the user or receiving an instruction from the user; 6, a controller for controlling the above-mentioned tracking unit 2 to the handset 5; and 100 is a communication terminal.
Also, in the figure, reference numeral 61 denotes a system switching function section; 62 is a control function section for the system 1; and 63 is a control function section for the system 2.
The conventional communication terminal operates as follows: Upon turning on a power supply of the communication terminal 100, the controller 6 first instructs an initial acquirement frequency inputted from the handset 5 by the user (or stored in the controller 6) to the receiver 3 to conduct xe2x80x9can instruction of wide-band acquiring operationxe2x80x9d of an electromagnetic wave which is relatively wide in received band (in the figure, those instructions are mentioned as xe2x80x9creceiver control signalxe2x80x9d).
Also, the controller 6 instructs the tracking unit 2 to xe2x80x9csearchxe2x80x9d the arrival direction of the electromagnetic waves simultaneously. upon receiving this instruction, the tracking unit 2 successively monitors a receive state signal (a signal indicative of a receive state such as a receiving signal strength or a bit error rate) obtained from the receiver 3 while changing the orientation of the antenna 1, thus controlling the direction of the antenna 1 so as to direct the antenna 1 to a direction excellent in the electromagnetic wave state. Further, the tracking unit 2 notifies the controller 6 of xe2x80x9ccompletion of searchxe2x80x9d after the antenna 1 has been directed in the direction excellent in the electromagnetic wave state. After that, the tracking unit 2 controls the antenna so as to maintain the direction excellent in the electromagnetic wave state.
Subsequently, upon being notified of xe2x80x9ccompletion of searchxe2x80x9d by the tracking unit 2, the controller 6 transmits the receiver 3 the receiver control signal which is called xe2x80x9cfrequency correctionxe2x80x9d to switch from the receive of wide-band electromagnetic waves to the receive of narrow-band electromagnetic waves with respect to the same initial acquirement frequency and to start a frequency shift correction of the subject communication terminal 100. The controller 6 confirms that the correction can be sufficiently made from the receive state signal obtained by the receiver 3 at a timing when the correction is completed.
Finally, the controller 6 transmits to the receiver 3 a frequency to be received for actually conducting communication which is inputted from the handset 5 by the user (or stored in the controller 6), as well as the receiver control signal which is called xe2x80x9cnormal receiving operationxe2x80x9d, thereby starting to receive the frequency for conducting communication (in this situation, the receiver 3 conducts the narrow-band receive and corrects the frequency by use of a correction value of the frequency shift which has been obtained in advance). The controller 6 evaluates a state of the line on the basis of the receive-state signal obtained at this time and then permits the user to conduct communication upon confirmation that sufficient receive can be made.
The communication terminal in the above-described conventional mobile communication system suffers from such a problem that when the user is switching from one system to another system, the acquiring operation of an artificial satellite is caused to be made as described above although the same direction must be maintained as it is because the same artificial satellite is used.
Also, there arises such a problem that the above-described frequency correction is caused to made, though the same frequency correction is applied because the same artificial satellite is used, the base station also uses the same reference frequency, and a deviation of frequency is the same.
Further, there arises such a problem that the above-described evaluation of a radio line is conducted although the possibility of having substantially the same quality of the radio line is high because the same artificial satellite is used, and the base station is also the same.
For those reasons, there arises such a problem that a period of time during which communication service is disenabled occurs for about 20 seconds in the above-described conventional communication terminal at the time of switching from one system to another system.
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a mobile communication system and a mobile communication method which enable a communication terminal to remarkably reduce an initial sequence by the application of a fact that systems to be switched therebetween have very similar electromagnetic wave environments.
In other words, in recent years, a large number of radio communication systems have been proposed, and commercial services have been started. Up to now, a communication terminal has been provided for each of those communication systems, however, a demand that a plurality of systems are utilized by one communication terminal is being increased. The present invention relates to a communication terminal which is capable of utilizing a plurality of systems, and an object of the present invention is to obtain a communication terminal by which the user can quickly receive a service with a reduction in a period of time required for switching from one system to another system.
A mobile communication system according to the present invention comprises: a radio base station for transmitting and receiving the electromagnetic waves of a first radio communication system and the electromagnetic waves of a second radio communication system; and a communication terminal having an antenna for transmitting and receiving the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system, a tracking unit for directing the orientation of the antenna to an arrival direction of the electromagnetic waves, a receiver for demodulating the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system which are received, a transmitter for modulating the contents to be transmitted into the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system, a handset for indicating predetermined information to the exterior and receiving an instruction from the exterior, and a controller for controlling the above respective units and implementing an initial acquiring procedure from which a predetermined procedure is omitted when a predetermined condition is satisfied at the time of switching from the first radio communication system to the second radio communication system.
Also, in the mobile communication system according to the present invention, the controller of the communication terminal implements the initial acquiring procedure from which a tracking procedure is omitted after the radio communication systems are switched when an arrival direction of the electromagnetic waves of the first radio communication system is identical with an arrival direction of the electromagnetic waves of the second radio communication system.
Further, in the mobile communication system according to the present invention, the controller of the communication terminal implements the initial acquiring procedure from which a frequency correcting procedure is omitted after the radio communication systems are switched when a reference clock of the first radio communication system is synchronous with a reference clock of the second radio communication system.
Still further, in the mobile communication system according to the present invention, the controller of the communication terminal implements the initial acquiring procedure from which a line evaluating procedure is omitted after the radio communication systems are switched when a base station of the first radio communication system is identical with a base station of the second radio communication system.
Yet still further, in the mobile communication system according to the present invention, the controller of the communication terminal also implements the initial acquiring procedure from which a tracking procedure and a frequency correcting procedure are omitted after the radio communication systems are switched when a reference clock of the first radio communication system is synchronous with a reference clock of the second radio communication system.
Yet still further, in the mobile communication system according to the present invention, the controller of the communication terminal also implements the initial acquiring procedure from which a frequency correcting procedure and a line evaluating procedure are omitted after the radio communication systems are switched when a base station of the first radio communication system is identical with a base station of the second radio communication system.
Yet still further, in the mobile communication system according to the present invention, the controller of the communication terminal also implements the initial acquiring procedure from which a line evaluating procedure and a tracking procedure are omitted after the radio communication systems are switched when an arrival direction of the electromagnetic waves of the first radio communication system is identical with an arrival direction of the electromagnetic waves of the second radio communication system.
Yet still further, in the mobile communication system according to the present invention, the controller of the communication terminal also implements the initial acquiring procedure from which a tracking procedure, a frequency correcting procedure and a line evaluating procedure are omitted after the radio communication systems are switched when a base station of the first radio communication system is identical with a base station of the second radio communication system.
Yet still further, the mobile communication system according to the present invention further comprises a communication satellite for relaying the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system between the radio base station and the communication terminal.
Yet still further, in the mobile communication system according to the present invention, the controller of the communication terminal implements the initial acquiring procedure from which a frequency correcting procedure are omitted after the radio communication systems are switched when a first reference clock of the first radio communication system is quasi-synchronous with a first reference clock of the second radio communication system.
A mobile communication system according to the present invention comprises: a first radio base station for transmitting and receiving the electromagnetic waves of a first radio communication system having a first reference clock; a second radio base station for transmitting and receiving the electromagnetic waves of a second radio communication system having a second reference clock which is quasi-synchronous with the first reference clock; and a communication terminal having an antenna for transmitting and receiving the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system, a tracking unit for directing the orientation of the antenna to an arrival direction of the electromagnetic waves, a receiver for demodulating the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system which are received, a transmitter for modulating the contents to be transmitted into the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system, a handset for indicating predetermined information to the exterior and receiving an instruction from the exterior, and a controller for controlling the above respective units and implementing an initial acquiring procedure from which a frequency correcting procedure is omitted at the time of switching from the first radio communication system to the second radio communication system.
Also, the mobile communication system according to the present invention further comprises: a first communication satellite for relaying the electromagnetic waves of the first radio communication system between the first radio base station and the communication terminal; and a second communication satellite for relaying the electromagnetic waves of the second radio communication system between the second radio base station and the communication terminal.
In a mobile communication method according to the present invention in a mobile communication system which conducts radio communication between a radio base station having a first radio communication system and a second radio communication system and a communication terminal using the first radio communication system and the second radio communication system in common, the communication terminal implements an initial acquiring procedure from which a predetermined procedure is omitted when a predetermined condition is satisfied at the time of switching from the first radio communication system to the second radio communication system.
Also, in the mobile communication method according to the present invention, the communication terminal implements the initial acquiring procedure from which a tracking procedure is omitted after the radio communication systems are switched when an arrival direction of the electromagnetic waves of the first radio communication system is identical with an arrival direction of the electromagnetic waves of the second radio communication system.
Further, in the mobile communication method according to the present invention, the communication terminal implements the initial acquiring procedure from which a frequency correcting procedure is omitted after the radio communication systems are switched when a reference clock of the first radio communication system is synchronous with a reference clock of the second radio communication system.
Still further, in the mobile communication method according to the present invention, the communication terminal implements the initial acquiring procedure from which a line evaluating procedure is omitted after the radio communication systems are switched when a base station of the first radio communication system is identical with a base station of the second radio communication system.